1. Field of The Invention
The present invention relates to a focal plane shutter of a camera conducting Through-The-Lens (TTL) multi-pattern light adjustment, that prevents light leakage between curtains.
2. Related Background Art
Conventional cameras capable of ordinary TTL light adjustment, have encountered exposure results of photographing that are widely dispersed depending on conditions of a subject since such cameras have the quantity of flashing light controlled so that the average value of exposure light across a specific area of film surface from which a photoreceptor device can receive lights, reaches a predetermined level when flashing light is adjusted.
For example, in the case of a camera where a photoreceptor device can receive lights from the area equal to the entire exposure area of the film surface, if a photograph is taken using light flashing in a field where a main subject occupies a small area and the background of the main subject constitutes a wide space, the portion that does not reflect the flashing light becomes wide, so that the quantity of flashing light so controlled may cause over-exposure for the main subject.
On the other hand, if a photograph is taken using light flashing in a field where an object of a high rate of reflection such as a gold-leafed folding screen is standing right behind a main subject in the case of the same cameras as above, the quantity of flashing light so controlled may cause, in contrast, under-exposure for the main subject.
To solve this problem, a TTL automatic light adjustment control device has been proposed as means for eliminating dispersion in the light exposure for a main subject due to difference between conditions of factors for subjects in the subject field such as the location and rate of reflection for such subjects in photographing using light flashing.
The automatic control device has a plurality of photoelectric means disposed at positions where the photoelectric means can receive lights reflected by the film surface, the plurality of photoelectric means each being capable of measuring the light reflection intensity from each of regions of the subject field obtained by dividing the subject field into one single central region and a plurality of peripheral regions.
Then, preliminary flashing of the flashing device is activated immediately before the focal plane shutter of the camera is opened so that the preliminary flashing light is firstly reflected by the subjects, as the image of the subjects, onto the lens-side surface of the shutter curtain of the focal plane shutter through the lens. The first reflected preliminary flashing light is secondly reflected by the lens-side surface of the shutter curtain of the focal plane shutter, then received and processed by the plurality of photoelectric means corresponding to the respective regions of the subject field.
The automatic control device integrates the light reflection intensity values outputted from each of the plurality of photoelectric means, and outputs these integrations as the detected values for the subject field rates of reflection based on the preliminary flashing light for the respective regions of the subject field.
Thus, the degree of weighting, or the weighting coefficient for each divided region of the subject field is determined such that the determined weighting coefficients enable an optimal exposure to be obtained for the main subject, by integrating computing the detected information on the rates of reflection for the respective regions of the subject field.
Successively, main flashing of the flashing device is activated immediately after the focal plane shutter of the camera is opened so that the reflected main flashing light is received and processed by the same plurality of photoelectric means as described above.
The automatic control device weights the light reflection intensity values of the main flashing that is outputted from the plurality of photoelectric means, with the weighting coefficient predetermined as described above.
The automatic control device then sums up and integrates the weighted outputs, and compares the integrated values of the weighted outputs with predetermined values. Thus, the automatic control device ceases the main flashing according to timing determined by such comparison, thereby completing the light adjustment of the main flashing. Such system of light adjustment is referred to as the "TTL multi-pattern light adjustment."
A focal plane shutter for the TTL multi-pattern light adjustment comprises four to five shielding blades and a driving mechanism therefor.
To conduct TTL multi-pattern light adjustment stably, it is effective to have an arrangement where the lens-side surface of shielding blades of a focal plane shutter is adapted to have a high rate of diffused reflection so that more reflection light strikes the plurality of photoelectric means described above. Thus, a focal plane shutter was fabricated with the lens-side surface of shielding blades thereof formed to have a high rate of diffused reflection, and was assembled into a camera capable of TTL multi-pattern light adjustment for photographing. With this arrangement, though no problems occurred in ordinary photographing, light leakage problems were encountered that light leaks through gap between overlapped edge regions of immediately adjacent and mutually overlapping shielding blades (hereinafter referred to as "light leakage between curtains"), thereby causing the film to be exposed adversely.